1. Field of the Invention
The invention relates to a control circuit for tuning a high-frequency input circuit in dependence upon a control voltage which directly controls a first adjustable component and at least indirectly at least one further adjustable component, in particular, for tuning a tuner for high-frequency equipment with an oscillator and at least one preceding preselection circuit, which are controlled in dependence upon a tuning control voltage, and, if necessary, with an amplification control voltage fed to an amplifier component, and with electronic tuning voltage control means and electronic stores.
2. Description of the Prior Art
In a known control circuit of this kind (German Offenlegungsschrift No. 2 854 852) for a tuner of television sets, the oscillator of the tuner is tuned in a PLL circuit. Subsequently, the individual preceding oscillating circuits which are to be tuned are switched over as further components via additional circuit arrangements into auxiliary oscillators which are again individually tuned successively via the PLL circuit with an altered divider ratio. In this case, the control voltage respectively derived from the tuning of the auxiliary oscillators is stored in analog stores as long as no change in the receiving frequency is desired. With this control circuit it is therefore necessary to directly engage the oscillating circuits preceding the oscillator in order to be able to switch them over as auxiliary oscillators. In addition to the substantial additional circuitry expenditure, there is also the danger of a mistuning of the oscillating circuits having occurred after the auxiliary oscillator circuitry has been switched off. Furthermore, the entire tuning voltage required for the tuning of the further components must be changed, for which purpose correspondingly variable voltage sources with the associated control range must be provided.